Through no doing of the Ensemble ACJW, its concert on Friday night at Zankel Hall took on a newsier aspect than might have been anticipated. Just a couple of weeks earlier the evening’s conductor, the young Spanish maestro Pablo Heras-Casado, still relatively unknown in New York, had been named principal conductor of the Orchestra of St. Luke’s, a major fixture in the city’s musical ecosystem.

So an audience heavily laced with music professionals was surely listening to Mr. Heras-Casado’s work with redoubled intensity. And he took the opportunity to make a distinctive impression, displaying a lively feel for dance rhythms in Bach’s Orchestral Suite No. 1; a volatile temperament, especially in music from Vivaldi’s “Griselda”; and a contrasting, similarly apt responsiveness to the languorous strains of Ravel’s “Trois Poèmes de Stéphane Mallarmé.”

But the real star of the evening, and undoubtedly the main draw for those music professionals, was the young mezzo-soprano Isabel Leonard. After the birth of her first child last year Ms. Leonard described herself as “forever a work in progress,” but there was little here that needed improvement.

She sang two arias from “Griselda” and another from Handel’s “Alcina” as well as the Ravel songs with consistently gorgeous tone and elegant demeanor. Her physical restraint suited the Ravel perfectly but seemed a bit strange in the Baroque numbers.

The “angry tigress” of Handel’s “Sta nell’Ircana” and the turbulent trills of Vivaldi’s “Agitata da due venti” virtually invite melodrama. Happily, Ms. Leonard avoided that, but perhaps by too wide a margin. She maintained an exquisite poise, leaving the drama to the voice, where it flowered richly in coloratura more expressive than the words themselves.

Mr. Heras-Casado led the ensemble of the Academy — a joint educational venture of Carnegie Hall, the Juilliard School and the Weill Music Institute — in an exemplary account of Schoenberg’s Chamber Symphony No. 2, which originated in his late-Romantic phase. Amiable and mellifluous by Schoenberg’s standards, the work develops conventional motifs in almost Beethovenian fashion in the first of its two movements and simply bandies them about for much of the second.

In Bach’s suite the strings — playing with limited vibrato, in line with current notions of period practice — never achieved ideal warmth, and the resulting straight tone mercilessly exposed minor flaws in intonation. The two oboists, ToniMarie Marchioni and Carl Oswald, were excellent, but the standout was the bassoonist, Shelley Monroe Huang (who also wrote the program notes), playing with superb agility and accuracy and with a full-bodied, chocolatey sound.